Distribution Box for the Emergency Power Distribution System
by Bryan A. Thompson
Last Updated 2/10/03
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This box was designed to prioritize loads and direct emergency power to them accordingly. It also provides some protection from the electrical transients that occur when grid power returns.
Inputs, Outputs and Controls
Wall Input - This is used to power the Always-On outlets when grid power is available. It also provides a control signal for the Time Delay Relay.
Generator Input - This is connected to the generator or other alternative energy source. It powers all outputs when grid power is unavailable.
Switch - This directs generator power to either the Override Outlets or the UPS Outlets, but never to both.
Always-On Outlet - This is powered by grid power if it is available, and generator power when grid power is not available. This is the highest-priority output.
Override Outlet - This is powered by generator power when grid power is not available and for 60 seconds after grid power returns, and not powered at all after the 60 second delay. The override outlets will only be powered when the switch is set to Override Output. This is a medium-priority output.
UPS Outlets - This is powered by generator power when grid power is not available and for 60 seconds after grid power returns, and not powered at all after the 60 second delay. The UPS outlets will only be powered when the switch is set to UPS Output. This is a low-priority output - it is only powered when the generator power isn't being used for something else.
Schematics and Other Notes
Distribution Box Parts List
Distribution Box Truth Table
Important: Don't build this unless you know exactly what you're doing! I have nothing, so suing me for your stupidity wouldn't get you so much as a food stamp!
Everything is waterproof except the outlets and switch. If I intend to take this out in the rain and leave it there, I'll add waterproof outlet covers and a waterproof switch cover.
Everything is rated for at least a 20A current load. The relays are rated for 30A resistive load (or a 1.5HP electric motor) at 120VAC.
Everything is secured to the face plate of the waterproof enclosure so that it can be removed for easy maintenance.